The present invention relates to computer systems. More specifically, the present invention relates to a method and apparatus for disabling power-on in a computer system that requires add-in modules.
High speed buses such as the Gunning Transceiver Logic Plus (GTL+) bus (Pentium Pro Family Developers Manual, Volume 1 Specification, published 1996) require the use of resistors at the physical ends of its electrical traces to properly terminate the bus. The resistors provide an electrical pull-up function and act as a lumped impedance load to minimize signal reflections off the ends of the traces. The Pentium II processor incorporates GTL+ bus termination resistors within the Single Edge Connector (SEC) cartridge enclosing the processor. A computer system designed to use two Pentium II processors is designed with the Slot 1 connectors located at the physical ends of each GTL+ bus trace. Therefore, when two processors are installed in a dual Slot 1 system, each trace on the GTL+ bus is properly terminated via the termination resistors in the SEC cartridges.
If a GTL+ bus operates with only one end of its traces terminated, the reliability of the computer system in which the bus is implemented on may be severely degraded. While a computer system may seem to be operating normally with an improperly terminated GTL+ bus, it is possible for data to be irreversibly corrupted without warning.
Operators of computer systems who attempt to terminate a GTL+ bus by inserting an SEC cartridge during or after powering up of the computer system may cause severe damage to the processor or the motherboard. Improper mating of electrical contacts on an SEC cartridge with electrical contacts on a connector on the motherboard during powering up may result in electrical shorts. In some instances, the electrical shorts may cause a serious safety hazard.
A computer system is disclosed. The computer system includes a bus. A first connector is coupled to the bus. A power lock-out unit is coupled to the first connector. The power lock-out unit prevents a system power supply from receiving a power-on request when a first module is not coupled to the first connector.